Investigators have zeroed in on what caused a plate on a moving walkway at Bangkok’s international airport to collapse in June, resulting in part of the leg of a 57-year-old Thai mum having to be amputated.

The lower part of Ms Suphannee Kittirattana’s left leg had to be cut off to extricate her from the machinery.

But on Sunday, her son said she was already taking her first few steps.

Professor Weerachai Phutdhawong, of Kasetsart University in Bangkok, said Ms Kittirattana’s leg fell through a plate that was being held only by worn-out screws as she was walking on the travelator at Terminal 2 of Don Mueang International Airport at around 8.40am on June 29.

The plate slid beneath the moving walkway and Ms Kittirattana’s leg fell through the gap and was sucked into the gear’s end of the walkway.

A report on Bangkok’s Channel 7 said the travelator had been in operation since 1987. It added that it was due for a replacement, but not till 2025.

A medical team had to cut Ms Kittirattana’s left leg off from above the knee at the airport.

Ms Kittirattana’s son, Krit, said in a Facebook post on Sunday that his mother was “learning to walk again” like a child.

“My mum walked for 15 minutes and must practise every day. It’s very encouraging.

“She’s still as beautiful as ever despite everything that has happened. I hope that soon she’ll be outrunning me,” he said.

He said earlier that the family was “most concerned about her mental state” and how she would adjust in the long term.

“This crisis is very hard for our family,” he said.

“We are still shocked and saddened every time we see the news or think of our mother’s condition, but we have to fight because our mother is fighting.”

He said his mother was planning to sue Airports of Thailand (AoT), the state-owned company that operates airports across Thailand.

A report in the Bangkok Post said the police were already examining footage from security cameras at the airport, after earlier slamming AoT for being uncooperative.